1. Field of the Invention
This invention relates to improvements in systems for heating and air conditioning helicopter cabins and particularly cabins of helicopters of the type driven by turbine engines.
2. Prior Art
Helicopters are particularly difficult to provide with environmental control systems because of the crowded and cramped space within the craft which leaves little space for necessary components of heating and air conditioning systems. This is particularly true with modern day helicopters driven by turbine engines.
It is known in large turbine-engine-powered helicopters to provide heating and cooling by a heat pump system powered by a separate turbine driven from the main turbine engine. However such a system requires that the main engine by operating and this creates problems when the cabin needs to be heated or cooled when the engine is off. Moreover, the system takes considerable energy and is quite complex and expensive.
It is also known to heat helicopter cabins utilizing a muff heater around the exhaust section of a turbine engine as shown for example in the patent to A. J. Casey U.S. Pat. No. 3,971,511 granted July 27, 1976. This system of the Casey patent utilizes recirculated cabin air mixed with outside air and in the commercial embodiment, pulls the heated air through the muff heater by a fan with its motor in a hot air duct. This hot air environment is disadvantageous for both the life and operation of the fan motor. Moreover, the Casey system provides only for heating the cabin and not for cooling the same.
It has also been previously known to air condition a helicopter cabin using the conventional components of a refrigerant type air conditioning system, namely an evaporator, compressor and condenser. However, such was not incorporated with a heating system so that some of the same components could be used for both heating and cooling. Additionally, when attempting to drive an air conditioning compressor from a turbine engine with a forwardly extending drive shaft e.g., such as on a Bell Helicopter Model 206 series, there appears to be no suitable mounting space for the compressor or space to take off for the compressor drive.